Digital
video recorders (DVRs) give you the ability to record perfect quality
pictures and replay them at the touch of a button. Digital recording
also make it possible to record video on a computer disk. DVRs are able
to record much more information in ether real-time or time-lapsed mode.
Real-time mode produces higher quality recordings that approximate the
ability of the human eye to easily distinguish moving images (60 images/second).
Time-lapse mode records more video over longer periods of time on storage
media. Since the number of pictures recorded per second in time-lapse
mode decreases significantly as the recording time increases, video
movement may appear jerky. Alarm recording combines these two modes,
recording in time-lapsed mode until an event occurs (operator selected
or alarm) that switches the recorder to real-time mode.
DVR
vs. Analog VCR
- VCRs use
standard VHS tape, while digital information can be stored on
digital audio tape (DAT), digital versatile disc (DVD), or hard
disk drive (HDD).
- DVRs have
the ability to search for recorded information based on time/date/second
as well as camera input, allowing for much faster retrieval
times.
- DVRs can
save images with very little background picture noise and higher
stability, and are generally of higher quality.
- With DVRs,
the image quality does not deteriorate during storage or frequent
viewing.
- DVRs require
less maintenance.
- DVRs offer
many additional features such as remote video retrieval, integral
multiplexing, pre and post-image enhancements, and networking
capabilities
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Types
of DVRs
Basic DVRs are a
replacement for traditional VCRs. They are typically single-channel
devices capable of recording up to one or two weeks of information.
Basic units offer little or no setup capability. The recorder usually
determines the playback quality, storage capacity, and reviewing characteristics.
Multiplexed DVRs combine multiple video inputs with
the recording unit, eight or 16-channel multiplexing unit with the digital
recording device. The time-sharing of video inputs operates the same
way as standalone video multiplexers. Multiplexed DVRs typically have
a storage capacity of about 480GB to 600GB.
Multi-channel DVRs are designed for high-end applications.
Requirements such as month-long storage, real-time video recording of
all video inputs and unlimited video channels can be obtained with multi-channel
DVRs. Multi-channel DVRs allow all images per camera to be recorded,
whereas, in a multiplexed unit, video inputs are divided between the
images. Multi-channel DVRs incorporate expandable storage devices that
range from DAT in jukebox configurations to a redundant array of independent
disks (RAID), each with the capability of supplying many terabytes of
storage.
DVR
and Remote Video Monitoring
DVR allows remote viewing of video systems through LANs,
WANs and Web-based systems. One major advantage of a network is the
ability to receive video signals anywhere using equipment ranging from
a simple Internet browser to special client-based application software.
Another advantage is that it eliminates the need to run new cabling
and provides easier solutions for future system expansion. Through system
integration and networks, the job of command and control by remote security
operators can be made more effective and efficient. Bandwidth management
is most important when considering a network video system. Digital video
recording and control over any network requires not only an understanding
of normal surveillance design parameters, but it also knowledge of Internet
and network topologies.
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